| 摘要: | 多孔矽奈米結構具有高表面積及物體吸附特性與半導體製程有良好的相容性，在先進科技發展中具有重要地應用，例如鋰電池電極、生物與化學感測器及太陽能電池之抗反射層。另外，其相對於矽塊材擁有較低的熱傳特性能，可應用於絕熱及熱電材料。常見的矽奈米結構製備方法包括如乾蝕刻、電化學蝕刻以及金屬輔助化學蝕刻。其中金屬輔助化學蝕刻具有製程簡易與設備成本低等優點，常見以貴金屬薄膜作為觸媒，再置入含有氫氟酸及氧化劑的混合液中進行蝕刻，然而對於觸媒型貌及分佈影響的研究相當少。本文選用白金作為金屬觸媒，具有優秀的催化能力及抗氧化能力。先以濺鍍方式於矽基材上沉積數奈米白金薄膜，再以熱退火方式改變金屬觸媒之形貌，進行金屬輔助化學蝕刻。研究探討製程參數對白金奈米粒子成長之影響，包括製程環境、時間、退火溫度及白金薄膜厚度。蝕刻後再探討白金粒子粒徑及分佈密度，與蝕刻後結構間關聯性。
在粒子成長方面，由實驗結果得知，相對高溫下可忽略製程環境及時間影響，退火溫度提升利於奈米粒子成長，奈米粒子對白金厚度變化最為敏感。在蝕刻方面，由結構截面發現奈米粒子粒徑並不影響結構蝕刻率。由結構表面發現影響表面形貌的關鍵為奈米粒子之分佈密度，分佈密度極高的情況下，蝕刻結構偏向多孔結構，且結構頂端有被蝕刻現象。而分佈密度較低時，結構則呈現柱狀結構，頂部則沒有被蝕刻。
;Porous silicon has high surface area and adsorption property with good compatibility with semiconductor fabrication, which can be applied to many advanced technology, such as lithium-ion batteries, biological and chemical sensors, and surface texturization in photovoltaic cells. It also has low thermal conductivity compared to bulk silicon, which is favorable as thermal insulation or thermoelectric materials. Numerous methods have been developed to fabricate porous silicon, such as dry etching, electrochemical etching, and metal-assisted chemical etching, The metal-assisted chemical etching is relatively simple and cost-effective, in which a thin layer of noble metal, served as a catalyst, is deposited on the smaple surface and then immersed in a mixed solution containing hydrofluoric acid and oxidant. Numerous studies have shown the fabrication of various nanostructures with different catalyst metal. However, the study on the effects of catalyst layer morphology is very rare.
In this work we use platinum as catalyst, due to its faster etching rate and better stability in disolution. The Pt film is thermal annealed to form nanoparticles flowed by the metal-assisted chemical etching to investigate its effects to the etching results. First we compared the size and distribution of nanoparticles in different annealing conditions with various atmospheres, annealing time, temperature, and platinum thickness. Then we observe the etching profiles using scanning electron microscopy. In the results, we found there are negligible effects in annealing time and atmospheric gases in high annealing temperature. And the higher the Pt thickness result the higher the nanoparticles size. In etching results, the etching rates are the same for various sizes of nanoparticles. The number density of nanoparticles is a key for structure morphology. Higher number density tends to form porous structures with some etching at the top of the structures, while lower number density tends to form columnar structures without etching at the top of the structures. |
